1. Field of the Invention
The present invention relates to a process for cleaning a harmful gas. More particularly, it pertains to a process for cleaning a harmful gas containing any of various alkoxide compounds and silane compounds that are used in the production step of a liquid crystal or a CVD step in semiconductor manufacturing process.
2. Description of the Related Art
With the continuous development of the semiconductor industry accompanied by a high degree of integration and miniaturization of the related products, there has been a steady rise in recent years in the amounts of alkoxide compounds typified by tetraethoxysilane and silane compounds typified by monosilane. In addition, pentaethoxytantalum which is an alkoxide compound has been brought into use in the CVD step as a raw material for a tantalum oxide film which is employed for a semiconductor device from a new compound or the like, for example, an interlaminar insulating film.
Most of the above-mentioned alkoxide compounds and silane compounds are highly toxic or unknown in toxicity and are combustible.
These alkoxide compounds and silane compounds are indispensable as raw materials or doping gases in the production process for silicon-based semiconductors and liquid crystals. At any rate it is necessary to remove a harmful component in the gas after being used in the semiconductor production process prior to discharge in the atmosphere.
As a process for cleaning a gaseous alkoxide compound, gaseous silane compound or the like contained in a gas, there are available two kinds of processes, one being the wet process in which harmful components are absorbed in an absorbing solution composed principally of an aqueous solution of an acidic component by the use of a scrubber; and the other being a dry process which makes use of activated carbon, a porous adsorbent of inorganic compound type, metallic salt supported on activated carbon, etc. (Japanese Patent Application Laid-Open No.207426/1991.)
However, the above-mentioned wet process suffers the disadvantages that when the equipment used therefor is large-sized, there is difficulty in post-treatment, it requires a considerable expense in the maintenance of the equipment and further that the absorption efficiency is not necessarily high, thereby making it impossible to immediately and completely treat a highly concentrated harmful gas at the present time. In addition the wet process brings about the problem of sludge formation due to the generation of a powdery oxide which is produced by the decomposition of tetraethoxysilane, monosilane or the like.
The dry process exemplified by the above-mentioned adsorptive treatment with activated carbon is disadvantageous in its low removing capability of harmful components and further requires a countermeasure against the possible hazard of causing fire when there are used a combustible or inflammable gas such as monosilane, and at the same time, a combustible gas such as hydrogen or a combustion-supporting gas such as oxygen each as a diluting or carrier gas.
Such being the case, there has long been desired the materilization of a process for cleaning a harmful gas, especially that discharged from the semiconductor industry, said process being enhanced in both treatment rate and treatment capacity for the harmful gas, excellent in removal performance, not only in an emergency when a relatively less concentrated, but a large amount of a harmful gas is leaked from a gas cylinder because of its abnormality, but also in the ordinary case where a harmful gas is discharged in a high concentration after being used in semiconductor production process, and free from the possibility of causing the hazard of fire in the case of gas cleaning or the clogging in a cleaning column due to sludge formation.